Production of thermoplastic films

ABSTRACT

An apparatus and method for producing rolls of film having no hard spots by slitting a tubular film with oscillating slitting knives and compensating for the fluctuation in the edges of the slit film due to the oscillation of the knives so as to obtain a reeled film having good edge register.

United States Patent 1191 '11] 3,801,036 Hasler v Apr. 2, 1974 [541 R TIN F THERM L I 2,868,541 1 1959 KOlOdZiCj 242/57.1

FILMS 3,323,740 6/1967 Blessing.. 242 57.1 2,989,265 6/1961 SClSlOd 24256.2 x [75] Inv Robm a g England 3,l88,856 6/1965 Schneider... 242 57.1x 3,536,273 10 1970 Hawkins 242 57.1 x [73] Awgnee' 'I F chem'callndusmes 2,666,598 1/1954 Robinette 242 57.1 London England 3,570,735 31971 Kurz 242/57.1 122 Filed: June 28, 1971 Primary Examiner-John W.Huckert [21 I App! 157306 Assistant Examiner-Edward J. McCarthyAttorney, Agent, or Firm-Cushman, Darby & Foreign Application PriorityData Cushman July 6, 1970 @1661 131116111 32671/70 57 ABSTRACT [52] us.Cl 242/56.2, 83/428, 242/55 1 51 1111. c1 Bh 35/02, B65h /02 Anapparatus and method for Producing rolls of film 58 Field Of Search242/562, 56 R, 56.6, 56.7, having no hard Spots by slitting a tubularfilm with [5 6] References Cited UNITED STATES PATENTS 3,365,992 l/l968Dreher 242/56 R cillating slitting knives and compensating for thefluctuation in the edges of the slit film due to the oscillation of theknives so as to obtain a reeled film having 1 PRODUCTION OFTHERMOPLASTIC FILMS The invention relates to a process and apparatus forslitting a travelling web and winding the slit web into a roll. Inparticular the present invention is concerned with slitting tubularfilm.

When a stationary knife is used to slit a web which is wound up to forma roll having good edge register, by which is meant a roll in which theedges are substantially aligned, the roll often has hard areas acrossits width which extend partly or wholly through the depth of the roll.The reason is because the web being wound up often has thicknessvariations across its width which may be termed high spots and lowspots." These tend to occur in the same position across the width of theweb as a result of variations in the processing conditions such as thevariation in the die gap producing tubular film or variation in thestretching conditions if an oriented film is being produced. When theweb is wound up these high spots and low spots are superimposed upon oneanother in the reel so that the high spots reinforce one another. Thehard areas resulting from the superimposed high spots, tend to stretchthe web in localized regions so that when the roll is subsequentlyunwound, the web has areas that are wrinkled. These irregularities makethe web visually unattractive and difficult to use in certainapplications such as printing and packaging. Consequently, the parts ofthe web containing these irregularities often have to be cut out anddiscarded, leading to a substantial wastage of material.

It has been proposed that this disadvantage may be overcome byoscillating the reel onto which the web is being wound transversely withrespect to the direction of travel of the web so that the high spots andlow spots are distributed across the width of the reel. However, thistechnique suffers from the disadvantage that the edges of adjacentlayers in the reel are not in register and it is necessary to cut offthe edges to get a satisfactory reel. This also leads to wastage ofmaterial.

According to the present invention we provide a method for slitting atravelling web of material and winding the slit webs into a reelcomprising slitting the web witha slitting means which oscillates acrossthe direction of travel of the web, and adjusting the position of theweb relative to the reel whereby successive layers of web wound onto thereel have their adjacent may be comprised of slitting units that arepartly or completely rigidly linked together so that part or all of theslitting means assemblyv moves in unison.

Examples of slitting units of the slitting means of the presentinvention include the cutting edges of knives, hot gas jets, wires orlaser beams. In one embodiment of our invention the slitting unitscomprise two knife edges which are rigidly linked together and move in aregular manner transversely to the forwardly moving direction of thefilm. By regular is meant that the movement of the slitting units iscontinuous rather than intermittent. However, it is not necessary forthe slitting means to move transversely or in a regular manner and ifdesired the slitting means may move irregularly and/or obliquely to theforward motion of the film. The number of slitting units used depends onthe number of separate pieces which are to be produced from the web; theseparate strips so produced may then be wound up individually. In apreferred embodiment of our invention a tubular film is slit into twowebs by two knives each of which slits only one thickness of film. Byvirtue of the tubular cross-section of the unslit film, each of the slitwebs includes an overturned edge which should be unfolded before theslit web is reeled up. In this embodiment the knives are preferablyoscillated out of phase with each other so that the widths of the twopieces of film produced by the slitting remain constant. The speed atwhich the slitting means moves is not critical providing there areseveral complete oscillations for each reel of film produced.

It is preferred that the amplitude of the oscillation of the knife isfrom 10 to 25 percent of the width of the advancing web as thisrangegives a suitable spread of any irregularities in the slit web. Otheramplitudes may also be used with good results but if the amplitude isless than about 10 percent of the width of the web, any

edges lying in a plane substantially perpendicular to the I longitudinalaxis of the reel.

The present invention is applicable to the slitting and winding of websof any material. In particular it is concerned with films ofthermoplastic materials which may be oriented or unoriented. Theinvention may be used for trimming the edges of fiat film or forslitting tubular film. ln slitting tubular film the slitting means mayoperate to slit through one or both thicknesses of the film. When onlyone thickness is slit it is necessary to unfold the overturned edge ofthe slit film before it is wound into a reel.

A reel made according to the present invention has substantially nodefects such as hard spots extending partly or wholly through the rollsince the high and low spots in the web are distributed across the widthof the roll.

The slitting means may further be composed of one or more slitting unitswhich may each move independently of each other. Alternatively, theslitting means thickness variation may not be dispersed enough while ifthe amplitude approaches about half the width of the web, the subsequentwinding-up of the web becomes increasingly cumbersome.

The position of the slit web may be adjusted relative to the reel togive good edge register on the reel either by oscillating the take upreel in response to the oscillatory movements of the slitting means orby means of a compensating device located between the slitting means andthe reel. The compensating device may be actuated in response to theoscillating movements of the slitting means by any suitable means, forexample a simple mechanical coupling between the slittingmeans and,compensating device, or preferably by an independent drive mechanismoperating in response to signals received from the slitting means toindicate the extent of the movement thereof. However, because ofvariations in the speed of travel of the web and the thickness of theweb, and the short period of time taken v by the web to pass from theslitting device to the compensating device, which requires virtuallyinstanta-.

neous response of the compensating device, we prefer that activation ofthe compensating device be effected in response to signals received froma sensor which senses the position of an edge of the slit web,preferably as it passes from the compensating device to the take upreel.

The position of one or both edges of the web or webs produced by theslitting operation may be sensed in any suitable manner. For exampletheir position may be sensed by light beams, by a pneumatic sensinggauge, mechanically or by capacitance determination.

The information obtained by the sensing means is relayed to acompensating device which adjusts the path of travel of the film toensure edge register on the reel. Our preferred form of compensatingdevice consists of at least two web guiding members which are capable ofpivoting in the plane of the forwardly moving web so that some or all ofthe film guiding members of the compensating device may pivot as oneunit in a plane parallel to the forwardly moving film. The web iswrapped around the guiding members as it passes from the slitting meansto the reelv Accordingly, the position of the web as it leaves theguiding members may be adjusted by altering the angle at which the webguiding members is inclined to the edge of the film as it is fed 'to themembers. Thus, by sensing the position of the edge of the web as itleaves the guiding members and relaying this information to a devicewhich controls the inclination of the guiding members to the web, thisinclination may be adjusted to compensate for the oscillation of theslitting means thus giving edge register in the reel.

The web guiding members of the compensating device may consist of rigidbars, rotatable rollers, sheets, or wires. It is important that the websurface does not become crinkled by thefilm guiding members and for thisreason we prefer that the guide member is a rigid bar rather than aroller. We prefer to maintain a thin cushion of air between the film andthe bar to prevent the film being scratched; this can conveniently besupplied'through holes in the bar. An assembly of such air bearing barsrigidly mounted on to a rotatable carriage as hereinbefore described iscommonly known as a bar guide. In one embodiment of our invention thebar guide consists of two such air bearing bars rigidly mounted on arotatable carriage so that they may be rotated as a single unit in aplane parallel to that of the oncoming film, in this way the transverseposition of the film issuing from the second bar may be displaced fromthe transverse position of the film approaching the first bar.

The compensating device is linked with a pneumatic sensing device and inthe particular embodiment of the bar guide type of compensating device,the sensing device is located such that the film passes through it almost immediately after passing around the second bar of the bar guide.The information received from the pneumatic sensor causes the bar guideto rotate as a single unit in a plane parallel to that of the oncomingweb so that the web is transversely displaced as is necessary to resultin a roll having good edge register.

The techniques of the present invention are: particularly suitable forslitting tubular film to flat form and may be used to produce one slitin a tube so that the tube may be opened out to a single sheet or toproduce two slits in the tube so that two sheets are produced. If twosheets are produced we prefer that each sheet is passed through a webguiding member as described to produce two reels each having good edgeregister.

The present invention is particularly useful for slitting films ofthermoplastic materials. Examples of suitable therrnoplastic materialswhich may be slit include polymers and copolyrners of olefines such asethylene, propylene, butene and 4-methyl pentene-l; polymers andcopolymers of vinyl chloride; polymers and copolymers of vinylidenedichloride; polymers and copolymers of styrene; polymers and copolymersof methyl methacrylate; cellulose and cellulose derivatives such as thecellulose-acetates; polyamides such as the various nylons and polyesterssuch as polyethylene terephthalate. The thermoplastic materials may alsobe coextruded so as to form film laminates. Other ingredients that maybe incorporated in the thermoplastic material include, for example,plasticisers, stabilizers, lubricants, antioxidants, processing aids,impact modifiers, dyes, pigments and antistatic agents.

The film may be unoriented or oriented as is desired. A common methodfor producing an oriented film is one in which the thermoplasticmaterial is extruded through an annular. die orifice in the form of athin walled tube or a tubular film, and stretched in the longitudinaldirection by passage through two pairs of nip rollers, the second ofwhich rotates at a greater speed than the first. The film may bestretched concurrently in the lateral direction by expanding it withinternal gas pressure.

The oriented film may be heat set by the techniques of roller heatsetting or by stenter heat setting, both of which are well known in theart. In theprocess of the present invention an oriented film mayoptionally be heat set before or after passage through the compensatingdevice. If the oriented film is to be heat set in a stenter, it ispreferably passed through the compensating device before passing intothe stenter.

The present invention is illustrated but by no means limited byreference to the accompanying drawings in which:

FIG. 1 is a schematic view of a flattened tubular film being slit with apair of rigidly linked knives that are moving in phase with each otherin a transverse direction to that of the movement of the flattenedtubular film.

FIG. 2 is a plan view of one layer of flat film issuing from the slitterknives shown in FIG. 1'.

FIGS. 3 and 4 are schematic plan views of the layer of fiat film shownin FIG. 2 being laterally displaced by a bar guide and subsequentlybeing wound up into a roll of film.

FIG. 5 is a schematic view of a flattened tubular film being slit with apair of knives moving out of phase with each other in a directiontransverse to that of the movement of the flattened tubular film, eachknife cutting only one thickness of the film.

FIG. 6 is a perspective view of one of the slit films issuing from theslitter knives shown in FIG. 5.

FIG. 7 is a simplified schematic view of a fluid logic sensing systemfor detecting the portion of an edge of a flat film and actuating acompensating device to adjust the position of that edge. I

Referring to FIGS. 1 and 2, a flattened tubular film 1 is slit into twoseparate layers of film by knife edges 2 and 3 rigidly linked together.The knives edges oscillate across the direction of travel of the tubularfilm and the extreme positions of the knives are represented by 2, 3 and4, S. The oscillation of the knives produces lay flat film 6 having theconfiguration shown in FIG. 2

. With reference to FIG. 3, the layer of film 6 is fed to a barguide asillustrated in FIG. 3 which comprises two bars 7 and 8 rigidly linkedtogether on a carriage 9 and are provided with air holes 37 in thesurfaces of bars 7 and 8 in communication with a source of air (notshown). Issuance of air through air holes 37 provides an air cushionbetween the layer of-film 6 and each of the compensator bars 7 and 8.The bar guide system is capable of rotational movement about a linethrough 10 perpendicular to the plane of the film. The film passesaround the upper bar 8 and around the lower bar 7 as shown and onleaving the bar 7, the film 6 passes through a pneumatic sensing device11 which is linked with the bar guide and causes it to rotate in such away that the film always issues from the second bar along substantiallythe same path and is thus wound up into a roll 12 having good edgeregister. FIG. 4 illustrates the bar guide at the opposite end of itsrotational movement from that shown in FIG. 3. Accordingly, due to theoscillation of the slitting knives 2 and 3 any thick spots in the filmare distributed across the reel and film that was produced according tothis embodiment of our invention was free from stretched areas caused bythickness variations.

Referring to FIG. 5, a flattened tubular film 13 is slit into twoseparate layers of film by knife edges 14 and 15 which oscillate out ofphase with each other across the direction of travel of the tubularfilm, the extreme positions of the knives being represented by 14, 15and 16, 17. v

The out of phase oscillation of the knives produces two lay flat films18, of which one is shown in FIG. 6.

.The overturned edge 19 of the film is then unfolded to yield a flatfilm suitable for winding into a reel.

Referring to FIG. 7, air or gas under pressure is introduced to acontrol unit 20 from a supply conduit 21 and passes into a manifold 22from which it flows into jets 23, 24 and 25 in sensing head 26 throughwhich travels an edge of film 27 in a direction perpendicular to theplane of the paper. The sensing head operates on the interruptable jetprinciple, the edge of the film, depending on its position, eitherpreventing or permitting air to pass from any or all ofjets 23, 24 and25 respectively to corresponding orifices 28, 29 and 30, and thence backto control unit 20, where the return flow of air is monitored and valve31 or valve 32 actuated as appropriate to pressurize either of chambers33 and 34 respectively in actuating cylinder 35 whereby piston 36, whichis coupled to the pivotable frame of the compensating device (notshown), is driven in the appropriate direction to compensate for wanderof the edge of the film as it travels through head 26.

It will be understood that all displacements shown, as well as the shapeshown in FIG. 2, have been greatly exaggerated to illustrate theprinciple of the invention.

1 claim:

1. A method for longitudinally slitting a travelling web of materialinto a number of separate slit webs and winding each of the slit websinto a reel, comprising contacting the traveling web with a slittingmeans, oscillating said slitting means across the direction of travel ofthe web, the amplitude of the oscillation being within the width of theweb, sensing the position of an edge of the slit web, adjusting theposition of the slit web relative to the reel, and winding the adjustedslit web onto the reel, whereby the adjacent edges of successive layersof slit web wound onto the reel lie in a plane substantiallyperpendicular to the longitudinal axis of the reel.

2. A method according to claim 1 in which a travelling web of materialis slit into a plurality of strips by slitting the web with a slittingmeans comprising a plurality of slitting units which oscillate acrossthe direc-- tion of travel of the web.

3. A method according to claim 1 in which the web is a thermoplasticpolymeric film. I

4. Apparatus for slitting a travelling web of material into a number ofseparate slit webs and winding each of the slit webs into a reelcomprising web-slitting means for oscillation transverse to thedirection of travel of the web, means for sensing the position'of anedge of the slit web, and compensating means responsive to said sensingmeans to adjust the position of the slit web relative to the reel,whereby the adjacent edges of successive layers of slit web wound ontothe reel lie in a plane substantially perpendicular to the longitudinalaxis of the reel.

5. Apparatus according to claim 4 in which the slitting means comprisesa plurality of slitting units.

6. Apparatus according to claim 4 in which the slitting means comprisesa pair of knife edges which are rigidly linked together and are movablein a regular manner transversely to the forward direction of travel ofthe film.

7. Apparatus according to claim 4 in which the edge sensing means is apneumatic sensor.

8. A method for longitudinally slitting a travelling tubular web intotwo separate slit webs and winding each of the slit webs into a reel,comprising contacting the travelling tubular web with two slitting unitseach of which slits only one thickness of the tubular web, oscillatingsaid slitting units across the direction of travel of the web, theamplitude of the oscillation being within the width of the web, sensingthe position of an edge of each slit web, adjusting the position of eachslit web relative to its reel, and winding each adjusted slit web intoits reel, whereby the adjacent edges of successive layers of slit web inthe reel lie in a plane substantially perpendicular to the longitudinalaxis of the reel.

9. A method for longitudinally slitting a travelling web into a numberof separate slit webs and winding each of the slit webs into a reel,comprising contacting the travelling web with a slitting means,oscillating said slitting means across the direction of travel of theweb, the amplitude of the oscillation being within the width of the web,wrapping the slit web around a compensating device, sensing the positionof an edge of the slit web as it leaves the compensating device, andpivoting said device in the plane of the forwardly moving slit web togive edge register of adjacent layers of slit web wound into the reel.

10. A method according to claim 9 in which a cushion of gas is providedbetween the compensating device and the web.

11. Apparatus for slitting a travelling web of material into a number ofseparate slit webs and winding each of the slit webs into a reelcomprising web-slitting means for oscillation transverse to thedirection of travel of the web, means for sensing the position of anedge of the slit web, and compensating means including at least two webguiding members which are capable of pivotal movement in the plane ofthe forwardly moving slit web, said compensating means being responsiveto said sensing means to adjust the position of the slit web relative tothe reel, whereby the adjacent edges of successive layers of slit webwound into the reel lie in a plane substantially perpendicular to thelongitudinal axis of the reel.

1. A method for longitudinally slitting a travelling web of materialinto a number of separate slit webs and winding each of the slit websinto a reel, comprising contacting the traveling web with a slittingmeans, oscillating said slitting means across the direction of travel ofthe web, the amplitude of the oscillation being within the width of theweb, sensing the position of an edge of the slit web, adjusting theposition of the slit web relative to the reel, and winding the adjustedslit web onto the reel, whereby the adjacent edges of successive layersof slit web wound onto the reel lie in a plane substantiallyperpendicular to the longitudinal axis of the reel.
 2. A methodaccording to claim 1 in which a travelling web of material is slit intoa plurality of strips by slitting the web with a slitting meanscomprising a plurality of slitting units which oscillate across thedirection of travel of the web.
 3. A method according to claim 1 inwhich the web is a thermoplastic polymeric film.
 4. Apparatus forslitting a travelling web of material into a number of separate slitwebs and winding each of the slit webs into a reel comprisingweb-slitting means for oscillation transverse to the direction of travelof the web, means for sensing the position of an edge of the slit web,and compensating means responsive to said sensing means to adjust theposition of the slit web relative to the reel, whereby the adjacentedges of successive layers of slit web wound onto the reel lie in aplane substantially perpendicular to the longitudinal axis of the reel.5. Apparatus according to claim 4 in which the slitting means comprisesa plurality of slitting units.
 6. Apparatus according to claim 4 inwhich the slitting means comprises a pair of knife edges which arerigidly linked together and are movable in a regular manner transverselyto the forward direction of travel of the film.
 7. Apparatus accordingto claim 4 in which the edge sensing means is a pneumatic sensor.
 8. Amethod for longitudinally slitting a travelling tubular web into twoseparate slit webs and winding each of the slit webs into a reel,comprising contacting the travelling tubular web with two slitting unitseach of which slits only one thickness of the tubular web, oscillatingsaid slitting units across the direction of travel of the web, theamplitude of the oscillation being within the width of the web, sensingthe position of an edge of each slIt web, adjusting the position of eachslit web relative to its reel, and winding each adjusted slit web intoits reel, whereby the adjacent edges of successive layers of slit web inthe reel lie in a plane substantially perpendicular to the longitudinalaxis of the reel.
 9. A method for longitudinally slitting a travellingweb into a number of separate slit webs and winding each of the slitwebs into a reel, comprising contacting the travelling web with aslitting means, oscillating said slitting means across the direction oftravel of the web, the amplitude of the oscillation being within thewidth of the web, wrapping the slit web around a compensating device,sensing the position of an edge of the slit web as it leaves thecompensating device, and pivoting said device in the plane of theforwardly moving slit web to give edge register of adjacent layers ofslit web wound into the reel.
 10. A method according to claim 9 in whicha cushion of gas is provided between the compensating device and theweb.
 11. Apparatus for slitting a travelling web of material into anumber of separate slit webs and winding each of the slit webs into areel comprising web-slitting means for oscillation transverse to thedirection of travel of the web, means for sensing the position of anedge of the slit web, and compensating means including at least two webguiding members which are capable of pivotal movement in the plane ofthe forwardly moving slit web, said compensating means being responsiveto said sensing means to adjust the position of the slit web relative tothe reel, whereby the adjacent edges of successive layers of slit webwound into the reel lie in a plane substantially perpendicular to thelongitudinal axis of the reel.